Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of a person's oxygen supply. Early detection of low blood oxygen level is important in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. A pulse oximetry system consists of a sensor applied to a patient, a pulse oximeter, and a patient cable connecting the sensor and the pulse oximeter. The pulse oximeter typically provides a numerical readout of the patient's oxygen saturation, a numerical readout of pulse rate, and an audible indication of each pulse. In addition, the pulse oximeter may display the patient's plethysmograph, which provides a visual indication of the patient's pulse contour and pulse rate.
Measuring a biopotential signal, such as an electroencephalogram (EEG) is also a widely accepted procedure for patient monitoring and diagnostic tests. An EEG measures cortical activity of the brain, which can reflect changes in cortical or subcortical cellular function due to insufficient oxygen or drugs, to name a few. For example, changes in EEG bandwidth and power can provide a measure of the effects of anesthetics on the brain. A biopotential measurement system consists of a bipotential sensor, a monitor and a patient cable connecting the sensor to the monitor. For example, an EEG monitor measures the potential difference between at least two well-spaced electrodes, using a separate ground electrode, and displays the resulting signal.